1. Field of the Invention
The present invention relates to a cryoablation catheter, and more particularly to a cryoablation catheter for creating long lesions.
2. Description of the Prior Art
Many medical procedures are performed using minimally invasive surgical techniques wherein one or more slender implements are inserted through one or more small incisions into a patient""s body. With respect to ablation, the surgical implement may include a rigid or flexible structure having an ablation device at or near its distal end that is placed adjacent to the tissue to be ablated. Radio frequency energy, microwave energy, laser energy, extreme heat, or extreme cold may be provided by the ablation device to destroy the tissue.
With respect to cardiac procedures, a cardiac arrhythmia may be treated through selective ablation of cardiac tissue to eliminate the source of the arrhythmia. A popular minimally invasive procedure, radio frequency (RF) catheter ablation, includes a preliminary step of conventional electrophysiology mapping followed by the creation of one or more ablated regions (lesions) in the cardiac tissue using RF energy. Multiple lesions are frequently required because the effectiveness of each of the lesion sites can not be predetermined with exactness due to limitations of conventional mapping. Often, five lesions, and sometimes as many as twenty lesions may be required before a successful result is attained.
Deficiencies of radio-frequency ablation devices and techniques have been overcome by ice mapping prior to creating lesions, as taught by U.S. Pat. Nos. 5,423,807; 5,281,213 and 5,281,215. However, even though combined cryogenic mapping and ablation devices permit greater certainty and less tissue damage than RF devices and techniques, both the cryogenic and the RF devices are configured for spot or roughly circular tissue ablation.
Spot tissue ablation is acceptable for certain procedures. However, other procedures can be more therapeutically effective if multiple spot lesions are made along a predetermined line, or a single elongate or linear lesion is created in a single ablative step. Radio-frequency ablation devices are known to be able to create linear lesions by dragging the ablation tip along a line while the ablation electrode is energized.
One problem associated with presently existing cryoablation catheters is that the outside dimensions of the cooling chamber must be limited by the size of the vessel. In other words, the outside diameter of the cooling chamber must be slightly smaller than the inside diameter of the vessel in order to permit passage of the cooling chamber through the vessel. Such small cooling chambers are relatively inefficient. It would be far better to have a cryoablation catheter with a large gas expansion chamber in order to increase the cooling efficiency of the device, however, large chambers may not be used within the rather small blood vessels of the human body.
The present invention provides a cryogenic ablation system including a cryoablation catheter which is particularly well suited for creating elongated lesions.
In accordance with one aspect of the present invention, there is provided a cryoablation catheter which includes an outer tubular member capable of insertion into the vessels of the body. An expandable cooling chamber, which preferably takes the form of a distendable balloon is disposed at the distal end of the outer tubular member. An inner tubular member is disposed within the outer tubular member and extends through a passageway in the wall of the outer tubular member. The inner tubular member serves to carry a cooling fluid to the interior of the expandable cooling chamber. A fluid expansion nozzle is disposed on the distal end of the inner tubular member. Preferably the fluid expansion nozzle takes the form of a Joule-Thompson nozzle. By applying a cooling fluid to the inner tubular member it is possible to expand the expandable cooling chamber while simultaneously cooling the chamber.
In accordance with another aspect of the present invention the fluid expansion nozzle takes the form of a Joule-Thompson fluid expansion nozzle. In addition, the cooling fluid preferably takes the form of a gas which, when allowed to expand, provides cooling at a temperature sufficient to cause cryoablation to occur at the surface of the expandable cooling chamber. One such gas suitable for this purpose is liquid nitrogen.
In accordance with still another aspect of the present invention, the inner tubular member extends through a passageway in the wall of the outer tubular member and the distal end of the inner tubular member is helically wrapped around the outer periphery of the outer tubular member at a position within the expandable cooling chamber. A plurality of holes extend through the wall along the distal portion of the inner tubular member and serve as exit ports for the cooling gas. This embodiment, applying a cooling fluid, such as liquid nitrogen, to the inner tubular member is possible to expand the expandable cooling chamber while simultaneously cooling the chamber.
In accordance with still another embodiment of the present invention, a cryoablation catheter includes a distal mapping electrode which is mounted on the distal tip of the outer tubular member in order to provide measurements of electrical signals within the chamber of the heart. These electrical signals generated at various locations within the heart serve to map electrical potentials within the heart. In addition, the cryoablation catheter may also include a second intermediate mapping electrode which is mounted on the outer tubular member and is disposed between the distal electrode and the expandable cooling chamber in order to provide a bipolar mapping function.
Accordingly, the cryoablation catheter system incorporates an expandable cooling chamber. The cooling chamber takes the form of distendable balloon which is disposed at the distal end of a catheter and also includes one or more tubes for delivering a cryogenic fluid into the expandable cooling chamber in order to expand the chamber to a desired size and to cause cryogenic cooling to occur within the chamber. By varying the pressure differential between the fluid entering the cooling chamber and pressure exiting the chamber it is possible to vary or control the size of the chamber. The same cryogenic fluid which is used to expand the cooling chamber is also used to create a cooling effect within the chamber, preferably by the use of a Joule-Thompson nozzle, positioned within the chamber. In another embodiment, the cryogenic fluid may be applied to the interior of the balloon by use of a tube which is helically wrapped around the catheter body beneath the balloon in which case the tube includes a plurality of side holes which extend along the tube for injecting the fluid into the cooling chamber.
The main advantage of the present invention is that the cooling chamber of this device may be deflated, or collapsed, prior to the insertion of the chamber into a vessel of the body. Once the chamber has been placed at a location where ablation is to occur, a gas such as nitrous oxide may be applied to the cooling chamber to thereby cause the chamber to expand to a point where it comes into contact with surrounding tissue. Simultaneously, the cooling gas may be injected into the expanded chamber to thereby cool the interior of the chamber, as well as the surface of the chamber itself to thereby cool adjacent tissue. As the adjacent tissue becomes sufficiently cool, this tissue will eventually freeze and ablation of such tissue will occur. Preferably, during this cooling cycle, the balloon or expansion chamber will become attached to the tissue in order to maintain the cooled surface in contact with the tissue.
Accordingly, with this device, it is possible for a physician to freeze larger surface areas, or alternatively longer surface distances, by use of the expandable chamber.
These and other objects of the present invention will become more apparent when considered in view of the following description of a preferred embodiment of the present invention.